Miniaturized Metamaterial-Inspired Travelling Wave Tube for S Band

Abstract

A miniaturized traveling wave tube (TWT) was studied by proposing a novel metamaterial (MTM) slow wave structure (SWS). The dispersion results show that n = −1 space harmonic of the fundamental mode exhibits the “forward” wave properties, which is the foundation of the MTM-inspired TWT. Meanwhile, the interaction impedance for mode 2 of the novel MTM SWS can be sharply decreased by introducing four blend edges to weaken the corresponding longitudinal electric field. Also, two coaxial couplers are presented to input/output the signals. The transmission results show that the reflection is as low as −15 dB from 2.90 GHz to 3 GHz, which ensures the amplified signal can be effectively outputted. The MTM-inspired TWT exhibits miniaturized superiority for its compact high frequency structure including the MTM SWS and the coaxial couplers. Especially, for the high-frequency structure, the transverse and longitudinal sizes are ~λ/5 and ~3λ, respectively (λ is the free-space wavelength at the operating frequencies). The simulation of the beam wave interaction shows that the proposed MTM-inspired TWT yields output powers of kW levels from 2.90 GHz to 3 GHz, with a gain of 23.5–25.8 dB and electronic efficiency of 14–22% when the beam current is 0.5 A and the beam voltage is 13 kV. The results indicate that the gain per wavelength is as high as 8.5 dB in the operating bands. The simulation results confirm that it is possible to weaken the backward wave oscillation from the higher mode in the miniaturized MTM-inspired TWT.

Cost-Efficient Two-Level Modeling of Microwave Passives Using Feature-Based Surrogates and Domain Confinement

“…This is primarily because EM analysis is able to accurately account for various phenomena exerting significant effects on circuit responses, such as EM cross-coupling [12][13][14][15][16][17]. Furthermore, the incorporation of size reduction techniques of various kinds (e.g., use of the slow-wave phenomenon [18][19][20][21], transmission line folding [22,23], defected ground structures [24,25], or multi-layer realizations [26][27][28]) makes the topologies of microwave devices increasingly intricate. Another important factor affecting their geometries is the implementation of additional functionalities, e.g., wide-band [29][30][31] or multi-band operation [32][33][34] or harmonic Electronics 2023, 12, 3560 2 of 20 attenuation [35][36][37].…”